The present invention relates generally to the field of electrical power conversion. The present invention relates more specifically to the conversion of Direct Current (“DC”) electrical power from an input voltage source to at least one output voltage which is controlled in reference to a neutral voltage where the neutral voltage is controlled in reference to the actual ground voltage located proximate to the conversion system (“Earth Ground”).
DC uninterruptible power supplies (“UPSs”) are typically used in data centers which store data and provide computing for many uses such as local and remote computing, internet data handling, intranet data handling, cloud computing, storage, etc. UPSs are also used for other applications such as DC micro-grid applications having a narrow range of DC voltage capability. In addition to having a narrow range of DC voltage capability, these applications must be reliable and operate as efficiently as possible to reduce the power consumption and heat generated by such systems. Recently, there has been a trend to move data centers near power plants due to the amount of power used by data centers and also move data centers in geographic areas having cooler ambient temperatures and wind patterns which reduce the energy needed to cool (remove energy from) the data centers. Accordingly, improving the efficiency of electrical systems and data centers results in substantial cost savings as a result of increasing the quantity of computing for a given amount of energy and reducing the amount of cooling required for a given amount of computing.
Information technology loads such as a data servers, network switches, data storage, etc., are required to be grounded to the actual ground proximate to the device (“Earth Ground”). The neutral and ground of the device are coupled together at the device, and then the neutral/ground are coupled to the Earth Ground (e.g. ground terminal at a data warehouse) through power buses/conductors which inherently have impedance. This impedance is the result of the resistance, capacitance and inductance of the electrical path between the neutral/ground terminal at the device and the Earth Ground (“Impedance to Earth Ground”). Typically power is supplied to the devices by UPSs and other power supply sources along with conductors coupled to neutral and Earth Ground. Accordingly, depending upon the operation and components of the device, the voltage of the neutral/ground at the device can differ from the Earth Ground which causes a current flow from the neutral/ground to Earth Ground. This current flow generates a voltage difference related to the Impedance to Earth Ground and the current. There can be substantial energy lost as a result of this voltage imbalance and current flow between neutral/ground and Earth Ground. Additionally, this voltage difference can impact the operation of circuit protecting devices such as the circuit breaker used to protect for overload currents, ground faults, and short circuits in the power conductors/buses of a data center.